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Aug. 31, 2011 -- As many as half of all people with a common and potentially lethal type of brain cancer known as a glioblastoma will have a seizure at some point during their illness.

Doctors often prescribe a drug to help control these seizures. But until now little was known about which drug, if any, is the best choice.

When added to standard treatment, an older seizure drug, called valproic acid (sold with the brand names of Depakote, Depakene, and Stavzor) may extend the lives of people with this type of tumor by an average of three months, a study shows.

The study is published in Neurology.

"Three months could be a big deal," says Keith L. Black, MD. Black is the chair of the neurosurgery department at Cedars Sinai Medical Center in Los Angeles. He reviewed the study for WebMD.

Glioblastomas are the most common type of brain cancer seen in adults. On average, people live 15 to 18 months after they are diagnosed with this cancer, Black says.

Standard treatment may include:

Surgery to remove as much of the tumor as possible.

Radiation therapy to the brain to shrink tumors.

The chemotherapy drug temozolomide (TMZ), which slows cancer cell growth. An anti-seizure drug is often added for those individuals who also have seizures.

"First, do no harm," Black explains. The hope was that the drugs would control seizures without dampening the effects of the other treatments.

Until now, no one was thinking that any seizure drug could actually extend the lives of people with brain cancer. "Valproic acid may actually offer an additional benefit besides protection from seizures," Black says.

Impact of Valproic Acid

The study originally set out to compare whether or not chemotherapy provides a survival edge when added to radiation among 573 people with brain cancer. It did.

Of 398 people who were also taking seizure medications, the 97 who took valproic acid lived three months longer than those who took other types of seizure medications. They also lived longer than those who had seizures but were not taking any medication to control them.

There were some side effects seen with valproic acid. These included a drop in the number of white blood cells that could increase a person's risk of getting an infection and a drop in blood platelets that could increase risk of bleeding. The survival benefit was only seen among people who received both radiation and chemotherapy. This suggests there may be a synergy between the chemotherapy drug and the seizure medication.

"It is now very important to go back and try to confirm and understand the mechanism," Black says.

"It is a curious observation," says Cormac O'Donovan, MD. O'Donovan is an associate professor of neurology at Wake Forest Baptist Medical Center in Winston-Salem, N.C. He is also a member of the Brain Tumor Center of Excellence Advisory Board at Wake Forest.

"The science behind it needs to be verified before suggesting this is the drug of choice for people with brain cancer and seizures," he says.